1. Field of the Invention
The present invention relates to an alignment detecting apparatus, and more particularly, to the apparatus for detecting an alignment condition between an eye to be examined having such reflecting surface that is approximately spherical surface or approximately toric surface, and a measuring system or the like.
2. Description of Related Art
As an examination apparatus for examining the optical characteristics of an eye to be examined, there is conventionally an ophthalmic apparatus such as a refractive power measuring apparatus (refractometer) , a corneal shape measuring apparatus (keratometer) and the like. As a detecting mechanism for an alignment condition of the ophthalmic apparatus, such mechanism is known that utilizes an image of the eye which is displayed on TV monitor for observation, and a corneal reflex (a image by corneal reflection) which is formed on the eye by projecting an alignment target. The alignment is performed by adjusting the vertical and lateral directions so that the corneal reflex may be a predetermined positional relationships relative to a reticle on the TV monitor, then by adjusting the working distance (forward and backward) so that the corneal reflex may be brought into focus while observing the corneal reflex which is displayed on the TV monitor.
Referring to above-mentioned alignment detection, an adjustment of a vertical and lateral directions can be performed easily, however, in the case of adjusting a direction of working distance, it is difficult to determine a direction where the point is moved in order to bring into focus.
Therefore, as an alignment detecting mechanism in a direction of working distance, such apparatus is proposed that judges an alignment condition by projecting an alignment light bundle from an oblique direction relative to the eye, then detecting a light bundle reflected by a corneal vertex with photo-receiving elements which are disposed on symmetric optical axes with putting an optical axis in a measuring optical system therebetween.
However, above-mentioned detecting mechanism has such disadvantages that the optical system thereof become complicated since the detecting mechanism needs exclusive optical systems which choose between an alignment light bundle for detecting a working distance and an alignment light bundle for detecting the vertical and lateral directions respectively, then detects each light bundle respectively.
Also, such detecting mechanism in a direction of working distance mentioned above has such disadvantage that an alignment detecting area is small.